A wire variety of lip type seals have been used in association with relatively rotatable machine elements for many years. Such seals have generally provided satisfactory and long-lived service in those applications involving little or no fluid pressure to be retained. However, as the contained fluid pressure increases, functional problems begin to arise in seal operation. Among the more common problems are accelerated lip wear and lip distortion. In more extreme cases, lip distortion can actually go so far as to fracture the sealing element or to allow the lip to turn inside out.
Numerous attempts have been made to overcome these and other problems with a variety of seal designs. Some measure of success has been achieved, but the results have not been fully satisfactory. For example, a variety of back-up members have been employed to prevent or reduce lip distortions. Also, low-friction lip liners have been utilized to reduce excessive lip wear. Examples of previous designs with back-up members are illustrated and described in U.S. Pat. Nos. 3,254,898, 3,495,843 and 4,300,778. Low-friction lip liners are shown in U.S. Pat. Nos. 3,495,843 and 4,289,321. While each of these prior art designs may provide some service improvement in high pressure sealing, each suffers from one or more shortcomings such as complex and expensive design, inability to function properly in low pressure applications or inability to accommodate shaft runout.
U.S. Pat. No. 3,495,843 illustrates a lip type seal having a low-friction resin liner and a backup piece designed to reduce lip distortion and/or reversal upon exposure to high pressure. However, the back-up piece or insert is a separate element which must be fabricated separately, which must be snapped into place and which can separate in service unless it is positively retained as by the plate shown in FIG. 2. It is also significant that the liner does not extend along the whole surface of the elastomeric element and there is no contact between the shell and the liner. The flex characteristics change abruptly at the end of the liner and thus may concentrate stresses in this area and bring about premature failure, particularly where there may be any degree of shaft runout.
U.S. Pat. No. 4,289,321 describe a lip type pressure seal having a PTFE liner. However, this is a dual lip seal and is designed to function between two (2) areas of pressure and to allow purging of pressure in one direction but not in the other. Again, there is no contact between the liner and the shell.
U.S. Pat. No. 3,254,898 describes another lip type pressure seal which appears to be similar to that of the present invention but which is significantly different in several respects. Among these differences, perhaps the most significant is the fact that there are really two (2) sealing lips and there is no bond between them thus allowing them to function independently of one another. Further, the old structure is of the assembled type and rather complex as compared to the present invention.
Other differences between these prior art designs and the present invention will be apparent to those skilled in the seal art.